I have a toshiba dst-3000 and a Sony 333ES receiver. I don't get frequent dropouts on those channels but do sometimes lose audio sync. I get lots of audio dropouts and frequent loss of sync on my local ota HD station (ABC affilliate which has all sound on their HD channel in 5.1).
I sometimes get audio stutter on regular directv channels which can be corrected by changing channels and going back again.
Keeping 5.1 audio synched with HD pictures seems to be an ongoing problem for broadcasters. HDNet only runs 2.0 and never drops out. They tried 5.1 for the winter olympics and couldn't make it work.